Having determined the molecular structures of lamprey hemoglobin at 2.0 A resolution and Glycera (blood worm) hemoglobin at 2.5 A resolution, it is proposed to elucidate as precisely as possible the alterations of structure which accompany the binding of ligands. The method of "difference Fourier synthesis" will be employed. Exploration of conditions for the preparation of X-ray quality crystals of leg hemoglobin from soya beans will continue. Having recently crystallized earthworm hemoglobin (mol. wt. about 2 x 10 to the 6th power it is proposed to bring these crystals up to X-ray quality and then determine their crystal lattice parameters. Having likewise recently crystallized rabbit muscle striated muscle actin, it is proposed to grow X-ray quality crystals and determine their molecular structure.